A. Field of the Invention
This invention relates generally to orthodontic appliances, and more particularly relates to the base portion of orthodontic appliances involved in direct bonding to a tooth.
B. Description of the Prior Art
The conventional method of orthodontic treatment has been through the use of metal brackets welded onto metal bands. The metal bands are mounted on the teeth requiring correction and an arch wire is attached to the brackets so that corrective forces may be applied to the teeth to properly position them within the dental arch. Problems associated with these bands include decalcification, patient discomfort and gingival irritation.
Bonding bandless brackets directly to the tooth surface was made possible as a result of the experiments by Buonocore in which tooth enamel was etched with phosphoric acid to enhance the bonding of adhesives to the tooth, (Journal of Dental Research, 34 (6) pp. 849-853, 1955).
A bandless bracket typically consists of two parts. One is the bracket body with grooves for accommodating wires which transmit corrective forces to the tooth. The other is the bracket base for supporting the bracket body and for bonding to the adhesive. Bandless brackets are made of metallic or plastic materials. While plastic brackets may be aesthetically pleasing they are too soft and deform during treatment. Plastic brackets may also discolor rapidly in the oral environment. Stainless steel brackets provide strength to withstand the forces required for the orthodontic treatment, but stainless steel brackets alone cannot be bonded effectively to the adhesive. In order to enhance the adhesion, Retief et al. (American Journal of Orthodontics 58 (1) p. 35, 1970) used brackets with slots in the bases to provide mechanical retention. U.S. Pat. No. 3,975,824 also described stainless steel brackets with undercuts to form a physical lock between the bracket base and adhesive. It is, however, labor intensive to produce these types of brackets.
It is also well-known in the art to use bonding pads which produce a mechanical interlock with the adhesive. Bonding pads are joined to the brackets by brazing, welding or sintering techniques. Brackets often are angulated on the bonding pads. Direct bond appliances with a two-part assembly are now widely used in the art.
Direct bond orthodontic appliances are attached to teeth by a widely used technique. This technique consists of three phases: applying the adhesive to the bondable surface of the appliance; putting the adhesive coated appliance onto the tooth; and cleanup of the residual adhesive.
Current orthodontic direct bond appliances are prone to fail in all three phases of the direct bond technique. Application of the adhesive to the current designs of bondable surfaces is sometimes difficult. Without a coherent layer of adhesive on the bondable surface, the appliance will fall off during treatment. Current appliances tend to skid or drift during placement on the tooth surface. Skidding destroys the initially polymerized adhesive and makes proper placement of the appliances difficult. Cleaning of residual adhesive expelled as flash from current design bases must be done with care. Improper removal of flash from the periphery of the base creates voids under the edge of the base. These voids create weak areas and lead to decalcification of the underlying tooth.
It is an object of the present invention to provide a new structure for the base portion of an orthodontic appliance for facilitating bonding of the base portion to a tooth, without the above described disadvantages.